BRAINCAKEThe Kekulé Model
In 1865 August Kekulé proposed a structure for benzene, C6H6: a ring of six carbon atoms joined by alternating single and double bonds, with one hydrogen atom on each carbon. In modern terms this would be cyclohexa-1,3,5-triene. Kekulé later suggested that the molecule switches rapidly between two equivalent structures in which the positions of the double bonds are swapped.
The model explained the formula C6H6 and allowed every carbon to form four bonds. However, it makes predictions that can be tested:
• Bond lengths: with three C=C bonds and three C-C bonds, there should be two different bond lengths, about 0.134 nm for C=C and 0.154 nm for C-C. The ring would be an irregular hexagon.
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Key terms in this lesson
- enthalpy of hydrogenation
- The enthalpy change when one mole of a compound reacts completely with hydrogen to saturate a carbon-carbon double bond, under standard conditions.
More in Arenes
- Benzene
- The Delocalised Model of Benzene
- Evidence for Delocalisation
- Combustion of Benzene
- Electrophilic Substitution
- Bromination of Benzene
- Nitration of Benzene
- Friedel-Crafts Alkylation
All 13 lessons in Arenes · All Edexcel A-level Chemistry topics